linux-kernel - Re: [PATCH v3 net-next] net: introduce a new tracepoint for tcp_rcv_space

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Date:   Mon, 23 Apr 2018 09:58:44 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     laoar.shao@...il.com
Cc:     eric.dumazet@...il.com, alexei.starovoitov@...il.com,
        songliubraving@...com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 net-next] net: introduce a new tracepoint for
 tcp_rcv_space_adjust

From: Yafang Shao <laoar.shao@...il.com>
Date: Fri, 20 Apr 2018 23:18:26 +0800

> tcp_rcv_space_adjust is called every time data is copied to user space,
> introducing a tcp tracepoint for which could show us when the packet is
> copied to user.
> 
> When a tcp packet arrives, tcp_rcv_established() will be called and with
> the existed tracepoint tcp_probe we could get the time when this packet
> arrives.
> Then this packet will be copied to user, and tcp_rcv_space_adjust will
> be called and with this new introduced tracepoint we could get the time
> when this packet is copied to user.
> With these two tracepoints, we could figure out whether the user program
> processes this packet immediately or there's latency.
> 
> Hence in the printk message, sk_cookie is printed as a key to relate
> tcp_rcv_space_adjust with tcp_probe.
> 
> Maybe we could export sockfd in this new tracepoint as well, then we
> could relate this new tracepoint with epoll/read/recv* tracepoints, and
> finally that could show us the whole lifespan of this packet. But we
> could also implement that with pid as these functions are executed in
> process context.
> 
> Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> 
> ---
> v2 -> v3: use sock_gen_cookie in tcp_event_sk as well.
>           Maybe we could init sk_cookie in the stack then in other code
>           path we just read it other than set it. If that is needed I
>           will do it in another new patch.
> v1 -> v2: use sk_cookie as a key suggested by Eric.

Applied, thank you.